There have been known various anionic surfactants useful as components of cleansing agents or cosmetics. It is known that surfactants have to excel in surface activities such as detergency and forming properties. However, with the recent diversification of consumers' needs or an increase in consumers' desire for high-quality articles, they are also required not only to be less irritating to the skin, ophthalmic mucous membrane or the like, but also to make products that are free from coloration or turbidity and give a more favorable feel to the skin. In addition, there is a growing tendency for consumers to require, from the standpoint of burdening the environment, that surfactants have good biodegradability and exert a surface active effect even when used in small amounts.
Traditionally, anionic surfactants such as alkyl sulfates, polyoxyethylene alkyl sulfates and alkyl benzene sulfonates have been used. However, many of these surfactants are not satisfactory in that they strongly irritate the skin at the time of use. Anionic surfactants that are highly safe and excel in biodegradability are amino acid surfactants such as, for example, long chain N-acyl amino-acid salts and derivatives thereof. These surfactants, however, are not satisfactory with respect to surface activity at low concentrations, and the coloration and turbidity of products containing them at low temperatures.
An example of a processes of the prior art for producing a long chain N-acyl acidic amino acid derivative is disclosed in JP-B-50-2973, in which an N-acyl amino acid menthol ester is obtained by dissolving, a long chain N-acyl acidic amino acid anhydride and menthol in toluol or benzol in the presence of p-toluenesulfonic acid as a catalyst at around 100° C. for reaction, and then neutralizing, water-washing and drying the reaction product. In this process, however, coloration in the resultant long chain N-acyl acidic menthol ester (light-yellow) is inevitable because the reaction temperature is high also, industrially implementing the process is difficult because the process involves complicated operations such as neutralization, water washing and drying.
In JP-A-2000-44554, there is disclosed a process for producing a surfactant composed of a long chain N-acyl acidic amino acid derivative, in which a long chain N-acyl acidic amino acid anhydride is reacted with a compound having a hydroxyl group or an amino group, just like the process disclosed in JP-B-50-2973 described above. In this process, in order to prevent coloration in the end product, the reaction is carried out at temperatures higher than the melting point of any one of the ingredients so that the ingredient is in the liquid state during the reaction, or the reaction is carried out in an inert solvent such as toluene while keeping any one of the ingredients in the liquid state. This process is, however, not a satisfactory one with respect to preventing coloration and the reaction yield (purity) of the end product.
For example, in JP-A-2000-44554, an embodiment is described in which N-lauroylglutamic acid anhydride and a sugar, such as sorbitol, or an amino acid, such as L-glutamic acid, are reacted without a solvent at a high temperature of 100° C. or more. In this process, formation of by-products is inevitable and coloration occurs in the product also, the reaction yield is too low to obtain the intended surfactant having high purity. The specification describes that the reaction can be carried out using an inert solvent such as toluene. However, when reacting N-lauroylglutamic acid anhydride and a sugar, such as sorbitol, or an amino acid, such as L-glutamic acid, the reaction has to be carried out at a high temperature of 100° C. or more so that the reaction is that of two phases, a solid phase and a liquid phase, since the solubility of these ingredients in a solvent is low. As a result, the process is not a satisfactory one with respect to the coloration and purity of the end product.
The present inventors have already disclosed in JP-A-2002-167313 an acyl group-containing composition (surfactant) that contains a long chain N-acyl acidic amino acid derivative produced by reacting one or more compounds which have, per molecule, m functional groups of one kind or more selected from the group consisting of hydroxyl, amino and thiol groups with a long chain N-acyl acidic amino acid anhydride, and a process for producing the same. The inventors have made sure that the resultant acyl group-containing composition has surface activity even at low concentrations and does not practically irritate the skin. However, the acyl group-containing composition obtained by this process is not satisfactory in that when it is neutralized and takes the form of an aqueous solution, significant coloration or turbidity occurs and its stability is not good. Further, the reaction yield of the composition is not satisfactorily high, and due to the high impurity content, the resultant composition has to be chromatographed to enhance the end product's purity.
In this reaction process, the reaction is also carried out at temperatures higher than the melting point of any one of the ingredients or by using an inert solvent, just like the process disclosed in JP-A-2000-44554 described above. Accordingly, when reacting a long chain N-acyl acidic amino acid anhydride with an amino acid in an inert solvent such as toluene, since an amino acid is hard to dissolve in solvents other than water, the reaction temperature has to be elevated to allow the reaction to proceed. As a result, by-products are inevitably formed due to the secondary reaction characteristic of the reaction, which causes coloration or turbidity in the end product.
Further, acyl compounds as the reaction products do not highly dissolve in a solvent, either, or have a high melting point. Therefore, in a reaction without a solvent or in an organic solvent, they can sometimes precipitate as intermediate products in the course of the reaction. Due to the necessity to prevent such a situation, the reaction temperature has to be set at around 100° C. or higher.
The present inventors have found that (i) one of the by-products formed in such reactions (reactions carried out at temperatures equal to or higher than the melting point of any one of the ingredients used or by using an inert solvent, just as disclosed in JP-A-2002-167313 and JP-A-2000-44554) has a molecular weight smaller than that of the acyl compound as the intended end product of the reactions by 18 and (ii) the by-product is hard to remove even by separating operations such as separation by chromatography. In fact, such a by-product could not be removed in a separation by chromatography conducted in the examples of the process disclosed in JP-A-2002-167313 and was a cause of coloration in the resultant acyl compound.
Thus, the drawbacks of the prior art lead to a first demand, that is, an acyl group-containing composition, as an anionic surfactant which is less irritating to the skin or the like and has a satisfactory surface activity even at low concentrations, and which contains a long chain N-acyl acidic amino acid derivative, wherein the composition contains a smaller amount of by-products, thereby being free from coloration and turbidity when it takes the form of an aqueous solution, and can be more easily produced in a high yield.
In the meantime, there are various kinds of gelatinous compositions, which are prepared by mixing an oil ingredient with an aqueous solvent and allowing the mixture to take the form of a gel. The term “gel” used herein means a form of compositions which contain liquid over a wide content range, such as a paste, a cream or a jelly, as described in The Basis of Colloid Chemistry, Dainippon Tosho, 1976: 245. For example, JP-A-55-141243 discloses an oily gelatinous composition which is prepared by using sodium stearate as a gelling agent and fat and oil as a mediator. The gelatinous composition thus prepared is not satisfactory in that its gel strength is not enough, and cracks are likely to occur in the composition. Moreover, because its hardness is fixed, it does not have arbitrary hardness.
JP-A-55-81655 discloses a gelatinous aromatic substance in which a water-soluble polymer compound, as a gelling agent, is generally added to make the composition gel. However, gelatinous compositions obtained by this process are not satisfactory in that when they are left at temperatures of around 40 to 50° C., their oil ingredients tend to separate or the polymerization degree of the polymers added tends to change which increases or decreases the viscosity of the compositions, and thus their stability deteriorates with time.
Examples of cosmetics which use gelatinous compositions include gelatinous cleansing agents. Such gelatinous cleansing agents are prepared, for example, by mixing an oil ingredient with an aqueous solvent and allowing the mixture to take the form of a gel. Then a water-soluble polymer compound known as a gelling agent is commonly added. When using a gelatinous composition formed with a water-soluble polymer compound for cleansing cosmetics, the resultant cleansing cosmetics are not satisfactory in that they do not spread well, their detergency is questionable and they are sticky even after washing with water. Moreover, their stability deteriorates with time as described above.
Meanwhile, there exists an oil gel which is obtained by making oil to gel with a gelling agent. However, the use of an oil gel makes it hard to adjust the viscosity of gelatinous compositions produced from it. Moreover, when using it for a cleansing agent such as a makeup remover, it cannot be washed from the skin with water, and it needs to be wiped off with tissue paper or the like after use and then cleaned off again with a facial cleanser, etc. There also exist gelatinous compositions which are water-in-oil emulsions. Also in this case, the oil phase is a continuous phase, and thus when using the compositions for cleansing agents, they need to be cleaned off the skin again with a facial cleanser, etc., just like the case of an oil gel. In either case, the hands become sticky with the oil ingredients, and the cleansing agent does not have a favorable feel.
Gelatinous compositions which are oil-in-water emulsions are also known. These types of compositions can be washed from the skin with water without a wipe-off operation as described above. However, their oil ingredients often remain on the skin and cannot be washed off completely from the skin using only water. Further, they have a poor compatibility with oily pollutants and their cleansing performance is not satisfactory. Thus, many compositions of this type have been examined while changing the kind or amount of the oil ingredient or surfactant used. However, there no compositions have been provided that are satisfactory in terms of stability and pleasant feel on the skin.
JP-A-10-219278 discloses compositions of anionic surfactants containing two long-chain acyl groups and two polar groups. The specification states that the compositions can take the form of a gel or a paste if desired; however, it discloses only aqueous solutions of the compositions as cleansing agents and does not describe the gelatinous oil compositions at all.
Thus, the above described drawbacks of the prior art led to a second demand, that is, a gelatinous composition which contains oil ingredients in a stable manner and can have arbitrary hardness in a range of the hardness of a paste to that of a solid, thereby overcoming the above described drawbacks.
Traditionally, cosmetics such as creams, milks and lotions have been allowed to contain a relatively large amount of moisturizing agents such as various types of oil ingredients or glycerol so as to leave the skin feeling moist or give the skin a sufficient moisturizing effect after their application. However, trying to leave the skin feeling further moist or giving the skin a better moisturizing effect often results in leaving the skin feeling excessively oily or sticky or makes the emulsified system unstable, which causes its separation with time, and hence the product deterioration. On the contrary, increasing the content of a surfactant so as to improve the stability of the emulsified system often results in increasing the irritation to the skin. Thus, it has been difficult to satisfy, at the same time, the moist feeling on the skin or the skin moisturizing effect of the composition, the better feeling on the skin after the application of the composition, and the stability of the products of the composition.
JP-A-10-203956 discloses cosmetics which contain a polyhydric alcohol and an amide compound having a specified structure, that excel in skin moisturizing effects, and will not feel sticky on the skin. However, the stability of its emulsified state is not fully satisfied.
JP-A-10-218754 discloses cosmetics composed of an anionic surfactant containing two long-chain acyl groups and two polar groups, powder and/or fine powder, and water. However, the cosmetics are not satisfactory with respect to stability, etc., though they feel better at the time of their application and have an improved skin moisturizing effect.
Thus, the above described drawbacks of the prior art led to a third demand, that is, cosmetics which excel not only in having a moist feeling on the a skin and a skin moisturizing effect, but also in being stable in an emulsified state.
There has been a tendency in recent years to use pigments, instead of dyes, as colorants for aqueous compositions for use in writing implements, recording instruments, printers or liquid cosmetics. This is because pigment colorants are superior in water resistance and light resistance. However, unlike dyes, pigments are insoluble or hardly soluble in water, and therefore it is necessary to disperse pigments stably in water. As dispersants used for this purpose, various types of nonionic or anionic surfactants, cellulose derivatives, or water-soluble polymers such as nonionic polymers have been used independently or in the form of a mixture. However, the method described above cannot disperse pigments well and is insufficient to cope with the occurrence of sedimentation or aggregation with time.
In oil makeup cosmetics, etc., it is generally necessary to disperse an inorganic pigment such as talc, mica, titanium dioxide or kaolin in an oil base material. However, such inorganic pigments are highly hydrophilic, and thus they do not disperse well in an oil base material, which causes problems such as deterioration of product quality.
For example, titanium dioxide is used in cosmetics to screen the skin from ultraviolet rays. The screening effect is produced when the particles of titanium dioxide are in a finely dispersed state. Accordingly, if the particles are not dispersed well and aggregate, the effect becomes insufficient. In delivery apparatuses for writing implements, recording instruments, printers or liquid cosmetics, sedimentation of pigments may cause problems such as clogging of the delivery portions.
Generally, the affinity of dispersants varies depending on whether the pigment is hydrophilic or hydrophobic, and therefore the effectiveness of the dispersion also varies. As a result, there has been no dispersant composition which has satisfactory dispersion stability to hydrophilic pigment and/or hydrophobic pigment.
Thus, the above described drawbacks of the prior art led to a fourth demand, that is, a dispersant composition which has a high dispersion stability with respect to hydrophilic powder and/or hydrophobic powder.